Following the URA paradigm [1]}, we assume that all the devices in arbitrary subblock \(l\)  exploit the same constellation \(\wp =\lbrace \mathbf {c}_1,\mathbf {c}_2,\cdots ,\mathbf {c}_{2^{B_l}}\rbrace \)  containing \(2^{B_l}\)  elements. Considering the angular space channel in (REF ) and the RIS to the BS reflecting channel \(\hat{\mathbf {U}}\) , the received signals of the \(l\) th subblock at the BS can be expressed as
\(\mathbf {Y}_l=\sum _{k=1}^{K_a}{\hat{\mathbf {U}}}\text{diag}(\mathbf {A}_\mathrm {R}\lambda _k)\mathbf {v}_l\mathbf {s}_{k,l}^H+\mathbf {W}_l,\) 
